Magnetic domain-wall storage and logic



March 30, 1965 D. o. sMlTH 3,176,276

MAGNETIC DOMAIN-WALL STORAGE AND LOGIC 22: ZEN "Tg2 "il/ M W x'/ ML' IRM x pil/LQ; if w N INVENTOR.

3&3 BY Donald O Smh C @aM/.Q @uw n@ 7 AGENT March 30, 1965 D. o. SMITH 3,175,276

MAGNETIC DOMAIN-'WALL STORAGE AND LOGIC Filed May :51, 1962 4 sheets-sheet 2 B31 l 1-1 15u' 1.11@ L W' D-l M1 11ML' INVENTOR.

Fl G. 6 BY Dona/JO. mi/v 14m/QM..

AGENT March 30, 1965 D. 0, sMrrH MAGNETIC DOMAIN-WALL STORAGE AND LOGIC 4 Sheets-Sheet 3 Filed May '51, 1962 INVENTOR.

DONALD O. SMITH Y QJ mm 1. I 4% mma/5o@ mo @ZE A N, wv Q Rl momnom m @ze/ F @mi Q LIIHJ mo m2@ Sama@ MSE@ /mw mmv Q 6d 226@ mm\ .E l Pd vm Q24 mhd@ Y a3 vv mo (wv z mi@ wwf Q24 k z mm\ Z Nm Q mkm mo mt www5@ N m a Nv 6v AGENT March 30, 1965 D. o. SMITH MAGNETIC DOMAIN-WALL STORAGE AND LOGIC 4 Sheets-Sheet 4 Filed May 31, 1962 Rin M @www Ww a m.0`h` 1 :.m ,w .9 9h61 m@ d/ N l D a a s z Y 0% 31:: S B

m/ 1 QQ V1 M 15 1 s 1 Q v E: :10E M 77; Ve A l 1x. H l m El .y :1:: 7 m mi El: e l v uw s tlbpao w A? .am *u s u AlunCaO 32V :2; w w Ell- AlhzH V .f IVNSH M AJZEZH IIFDL'DO AGENT United States atent 3,17 6,27 6 MAGNETIC DOMAIN-WALL STRAGE AND LGIC Donald 0. Smith, Lexington, Mass., assignor to Massaeh'u'setts Institute of Technology, Cambridge, Mass., a corporation of Massachusettsl Filed May 31, 1962, Ser. No. 199,113 6 Claims. (Ci. 340-174) This invention relates to thin film magnetic data processing and more particularly to magnetic domain-wall storage and logic devices.

Present day large .capacity data storage systems generally use magnetic storage devices which operate on the principle that if a given magnetic domain configuration is stable, so is the one which corresponds to a reversal in direction of all these domains. This principle is common to magnetic storage of binary information on drums, discs, toroidal cores, tapes or thin films. In such cases in which the storage mechanism is the direction of magnetization of the magnetic medium, magnetization in a particular direction determined by the geometry of the element may be assigned the significance of binary ONE and magnetization in the opposite direction the significance of binary ZERO. Such bistable magnetic devices have ,also found use for delaying and shifting information, usually in cooperation with circuit elements such as diodes which direct the fiow of information in the desired direction.

The present invention has as its primary object the provision of a novel magnetic storage mechanism which permits a reduction in the amount of magnetic material involved with a reduction in space and power for a given amount of stored-information. A further object is to provide a magnetic media suitable for logical operations.

These and other objects of the invention are achieved through the use of thin strips of magnetic film material in which information is stored as the sense of magnetic rotation within the domain walls separating adjacent magnetic domains having opposed directions of magnetization. Local magnetic fields are employed to inject magnetic domains into the strip material so that the magnetization within the interdomain walls is given a predetermined sense of rotation. Local magnetic fields are also employed to shift the position of injected domain walls along the strip to new locations in successive steps by a controlled amount. The invention also contemplates combining thin strips of magnetic film material interconnected in predetermined arrangements to provide a basis for logic operations by the controlled shifting of data through the interconnections and subsequent interaction between domain walls.

The invention likewise involves several features and details hereinafter described and illustrated in the accompanying drawing showing the invention in preferred embodiments wherein:

FIGURES 1A and 1B illustrate domain wall storage.

FIGURES 2A through 2D illustrate domain wall injection.

FIGURES 3A through 3F illustrate domain wall shift- FIGURE 4 illustrates the schematic diagram of a circuit for the storage of binary information.

FIGURES 5A through 5R illustrate the processing of stored data.

FIGURES 6A through 6D illustrate the process of addition -and'erasrure of stored data.

FIGURES 7A through 7C illustrate complementation.

The concept of a domain wall in a ferromagnetic material is illustrated in FIGURE l where a strip 11 of magnetic film material is assumed to have been treated to obtain an easy axis of magnetization transverse to the length ICC of the strip, i.e. preferentially to align the electron spin axis substantially perpendicular to the length of the strip. Following the application along the strip of a uniform strong magnetic field along the easy axis, a single magnetic domain may remain. If the magnetizing field along the entire length of the strip is reversed, the direction of magnetization of the entire strip is reversed. If a local reversing field is applied, only a local intermediate region will reverse its orientation and the result is a magnetic domain 12 lying between domains 13 and 14 and having a direction of magnetization shown by arrows 15 opposed to the initial direction of magnetization shown by arrows 16; the boundaries between regions 14 and 12 and between regions 13 and l2 are represented by interdomain walls 17 and 18 of finite thickness. Centrally of the finite wall thickness the electron spin axes are represented by arrows 19 perpendicular to the easy axis of the strip while on either side they conform to the mutually opposed orientation of respective bordering domains. Accordingly, intermediate the two sides of the interdomain wall, the electron spin axes assume every transitional position required for a reversal of direction.

In viewing the transitional positions within wall 17 as a rotation from domain 13 to domain 12, the sense of domain wall rotation is counter-clockwise. However, the rotation from domain 12 to domain 14 within wall 13 is in a clockwise sense. It is this sense of rotation within the interdomain wall which is controlled in the present invention and used for information storage.

Where two domains such as 12 and 13 are-uniformly magnetized in opposite directions and are separated by a magnetic wall such as 17 in which the magnetization is rapidly varying in direction, there are two limiting cases of the spatial variation within the walls. In FIGURE 1A the interdomain magnetization rotation is in the plane of the film and perpendicular to the wall. This is known as Neel type wall and it occurs in films having a thickness in the region of 200 A. InFIGURE 1B the interdomain magnetization rotates in the plane of the wall. This is known as a Bloch wall which occurs in films having a thickness in the region of 2000 A. For film thicknesses intermediate these values, the wall spin axis orientation may become complicated, as is the case with the crosstie wall described by Huber, Smith and Goodenough, in a paper, Domain Wall Structure in Permalloy Films, Journal Applied Physics 29, 294, 1958.

While the following description illustrates the use of the Neel wall inv practicing the invention, since both the Neel wall and Bloch wall demonstrate that the domain wall rotation can be in either a clockwise or a counterclockwise sense, the principles involved yare equally applicable to the Bloch walls and the use of other type walls is not precluded.

In order to be useful as a storage medium, walls of known sense must be injected into the magnetic film, the stored information must be shifted in order to proceed with the storage of information, and a method of extracting the stored information from the magnetic film is required. l

Referring now to FIGURE 2, the method of injecting domain walls of controlled sense of rotation into a thin film magnetic storage element is illustrated in diagrammatic form. As specified previously, strip 11 of magnetic lm material is assumed to have been treated to have an easy axis of magnetization, A, transverse to the length of the strip with a remanent magnetization in the direction of arrows 16 and to have a` thickness such as to acquire Neel walls. A conductor 21 is shown lying above strip 11 at an angle of approximately 60 to the easy axis of magnetization and electrically insulated from strip ll. A current flowing through conductor 21 inthe direction indicated by arrows 22 will produce a magnetic field at the strip which is in the direction indicated-by arrowsH. Thus input current to conductor 21 has been` given a direction such that the field produced by'leg'23 is diminishes with distance along strip `11 and becomes zero' atvtwo regions 17 and 18 lying between leg 23 and legs s, 1 raam Rather than moving strip 11 physically with respect to conductors 21 and 26, the pattern of alternately magnetized domains can be propagated through the magnetic w film by the application of local magnetic fields strong 24 and 25. In Vtransition regions 17 and 18 the electron Y i spin axes Yassume energy transitional position required to `executethe reversal of vmagnetization as shown by the arrows placed thereon.

FIGURESZA and B illustrate two possible states of remanent magnetization in stripY 171 and the direction of current fiow in conductor 21 vrequired to inject domain walls therein. YIt is to be noted that the sense ofy rotation of the electronvspin axes is in the same counter-clockwise directionA going from domain V13 to domain 12 through wall 17 in both cases. In like manner, it is evident that the same clockwise sense of rotation is found in wall 18 going from domain 12 to domain 14. Thus, it is established that the same sense of rotation yof the'magnetizaproper direction to producev a local field having a direc-l tion to reverse the magnetization ina discrete local zone of strip 11, regardless of the initial direction of magnetizawill always inject an interdomainl rotation having thev significance YN when energized to cause domain 12. to be main 13. j Y f v In order to'changethe sensel of interdomain rotation f tion within Vthedomain walls 17 and 1S is obtained by Venergizing conductor 21V witha current iiowing in the enough to move domain wallsbut tooweak to inject domain Walls.l In orderito shift the information to the right, localmagnetizing fields -H in the vicinityv of the domain walls and having directions shown by the'arrows as shown in FIGURE 3B are provided. Under the infiuence of the local fields, a force is exerted which Vwill move the domain walls to the right to the stable position of H= asshown in FGURE 3C. Then in the same manner, a second local field configuration as illustrated by FIGURE 3D, is provided to produce a'second shift of the domain walls( tothe right as shown in FIGURE 3E. FIGURE 3F represents the next local Vlfield configuration tocontinue shifting the domain walls to the right. Since the propagating fields'arerbelow the initial valueto estabiish new domains,'the information pattern is caused to move in ldiscrete steps along the strip. Obviously the direction of information iiow Vcan be reversed by reversing the field polarity shown in FIGURES 3B, C and F.

A practical scheme for obtaining the Arequired local field patterns to perform the operations of writing or read-inf and shifting is shown in FIGURE 4 which is a schematic diagram. A top view of the ferromagnetic strip 11. is shown. VThisis a thin film of magnetic material, such as permalloy, deposited toa thickness of ap- Y proximately 100 A. on a substrate (not shown in the vreversed in magnetization from the magnetization in dov with local domain injection, it is necessary to change` the i orientation of the conductor with respectto the strip 11` asis shown in FIGURES 2C and 2D wherein only the center legis'shown for ,the sake of simplicity. In this case, current Yflow as shown by arrows 22in a ,directionV -to cause domain injectioninstrip 11 willintroduce wall energizedto produce domain injection'and thedirection Y of current fiowin a selected conductor in order to obtain 'domain injection is specified by the previous operation performed on the magnetic material ofthe strip.

Assumingthat conductors 21 and 2-61occupythe`rsamei Yposition-in space and that the'` strip k11 can be moved in interest of simplicity). As in FIGURE 2, winding 21 is provided to inject domain walls in the controlled sense to signify the digit N and winding 26 is provided to inject domain walls to signify VtheV digit P. Windings 21 and 26 are insulated electrically from each other and the filmY strip `'11. Although ground connections are omitted from FIGURE 4 in the interest of simplicity, windings 21 and 2,6 are shownV `terminated at points G which are understood-to4 join ypoint G connected to drive current sources dfand 45. The two shift windings 27 j `ring :baclr to FIGURE 4, a source `of timing pulses 41 to l Y I i i control the sequence ofoperations is shown connected to a This means that the orientation-of the conductor with ,respect tothe strip controlsthesense of the 'interdomain' wall rotationV which is'obtained when the conductor isr ring counter 42to provide a four Vstep operation by apply- Ving pulses to leads -1, 2, 3', 4 in response-to successive either gate 46 or gate 47 is energized alternately. Since i the writewindings Zliand 26 and the shift windings 27 and discrete steps with respect to conductors 21 and 26 soy that the position ofY zone 12 isY moved-to the place Yof,YV

zone 13 and zone 14 totheplace of zone12 and soon; then` binary information can befstored'in stripV 11VV as a vconductors'zl for'fNiand conductors 26 for PJ The ,regular pattern of alternately magnetized domains carries no information but merely serves to4 space the information I. stored in the walls; a pattern of`iinformatiori NlNNPPV is shown in FIGURE 3A, scanning ,from right to left. Here strip .11.' is shownV with a number of Vdomains with a pattern of ialternate'directions of magnetization shown by arrows spaced by domainwalls' identified asrfP' or N Vin accordance withthe stored information. l Within do-V 'main walls theA electron spin Vaxes in the centerj part 4of the wall are represented'by-arrows.Y

28 requirecurrent'flow in 'both directions alternately, YUP drive'current source `i4-and DOWN drive current source "'45 are'A provided,v "UP and j DOWN are adopted to signify'the vdirection of current fiow in the several windings 21, 26, 27, 28 which produce magnetic field-s in UP,and"DOWNftdirectionsaccording to the :diagrams ofi-FIGURES;y The output of gate 46is fed to AND gates `51, 53, 55, and 57, while-the output of gate 477v is fedto-AND gates 52, 54, `56,1and 5S.v Input 'Vdataipulses from source 40 are fedY directly through level j clip ycircuit 48 to ;AND, gates 51 and 52 and through inpulse on line 1 hasv triggered flip-nop 413 to render-gate 46 verter 49' throughlevel clip circuitfSt)VA to AND gates VV53' and 5.4. i

Assuming that the region of strip 411 -be1f1eath the write windings 21 and .26 has beenv `placed-in a niagnetized state so that the direction of magnetization isin an UP direction, Yas in domain 3ft-of FIGURE-3A, and that a conducting, then va vpulse on vlinev 2Hwillffbe applied to V4TAND gates 51, 53, .55, and 57. However, the first pulser of datais an N; so V'that only gate 53 is energized data pulse UB, drive currentfand aV timing pulse simultaneously. Consequently, the UP drive current is applied through AND gate 53 and OR gate 62 to write winding'Zl. A domain 31a is there-by injected in strip 11 and the domain wall 32a between domain 30 and domain 31 is given a clockwise sense of rotation.

The third timing pulse on line 3 of counter 42 is applied to AND gates 55 and 56. UP drive current is, therefore, applied through gate 5S and OR gate 63 to winding 27 in a direction to move domain wall 32a to theright along strip 11 to a position beneath winding 2S.

The fourth timing pulse on line 4 of counter 42 is applied to AND gates 57 and 5S. UP drive current is now applied through gate 57 and OR gate 64 to winding 28 in a direction to move domain wall 32a a second step to the right along strip 11.

As noted earlier, the fields required to shift domain rwalls may ybe lower in intensity than the fields employed to inject domains, so resistors 65 are shown shunting shift windings 27 and 28 as a reminder that windings 27 and 28 lare driven to produce lesser local eld intensities if the same current drive source is used for the write and shift operations.

The next timing pulse appears on line 1 of counter 42 to trigger flip-flop 43 which in turn energizes gate 47 and makes ga-te 46 non-conducting. The sequence of operations can now be repeated with current iiow in the DOWN direction. The next data pulse being P will not r52, when energized by a pulse on lead 2, the P data pulse and DOWN current source 45 will apply a current to Write winding 26 through OR gate 62 to inject domain 31b with :a magnetization in the DOWN direction and having a :domain wall 32h with a counter-clockwise sense of rotation. When lead 3 is energized domain walls 32a and 32h are both shifted again to the right by the DOWN current in shift winding 27 and energize.- tion of lead 4 in turn advances domain Walls 32a and 3221 one more step along strip 11 to the right.

Pulsing line 1 of ring counter 42 now triggers flip-flop 43 to change drive current sources back to "UP. The Isequence of operations is then repeated. Briefly, the sequence is: (1) reverse the drive current flow, (2) wri-te information, (3) shift all stored data one step to make `room for the next bit of data, (4) shift all stored data tok make room to shift the next bit of data. In the maner described above, the remaining N, P and P data pulses are stored by alternate directions of current flow in windings 21 and 26 respectively and the stored data is shifted to obtain the pattern of FIGURE 3A in which alternate domains .are magnetized' in alternate directions and the stored information is carried by the sense of rotation of the interdomain walls.

IIt may also be noted that it its possible to 'write and shift at the same time during one of the shift operations. Ther sequence of operations may then be thought to be: (1)*shift all stored data one step to the right to clear the write zone, (2) reverse the direction of current ow, (3) write next data bit and shift all previously stored data; back to (l) shift all stored data including that just previously injected, etc.

It isl obvious that the required sequence of switching operations can be obtained in a great variety of circuitry ywell rknown to the computer and communications field and that mechanical switches or relays can serve the purposes where high speed of operation is not needed.

In connection with FIGURE 4, by way of example, strip 11 may be 0.005 wide and placed on a substrate 1.0 long. Windings 21, 26, 27 and 28 are limited -at present to the resolution which etched wiring techniques permit, conductors of the order of 0.005" spaced by y 0.005 are readily obtained. This permits current density in the conductor which is more than ample to develop the I local fields of the order of 2 oersteds which are required to injectdomains and to shift domains.

Under those conditions, the domain walls are found to be of the order of one micron spaced by domains whose size 0.005 corresponds to the conductor. The time required to inject domains is of the order of 10-50 millimicroseconds while the time to shift domain walls, of the order of 200 millimicroseconds, llimits the speed of operation.

It is evident that the dimensions used to illustrate the embodiment are not inherent limitations of the process of storing information by means of the controlled sense of domain wall rotation but rather are limitations of the techniques readily available by which the process is demonstrated. Indeed, the magnetic domain wall storage process is visualized as providing the maximum ultimate in- Iformation storage capacityobtainable in magnetic mater-ials.

It is further evident that the ring counter 42 may be provided with any desired number of output leads to provide for additional timed operations which may -be performed on the stored data at specified times and places as =will be discussed later; and that once the stored data has 'been shifted along strip 11 out of the inuence of the write windings 21 and 26, certain operations `may also be performed on the stored data at the same time that data is being written.

Once the operations of injecting domain walls of controlled sense and of shifting the position of the domain walls along the strip are made available, then it becomes possible to make use of other properties of domain walls to manipulate the stored information to perform logical operations. One of these takes advantage of the fact that two domain walls of opposite `sense if moved together will destroy (unwind) each other; however, walls of the same sene when brought together do not necessarily destroy each other, but can form a double wall which can subsequently be separated again into two single walls. Thus, erasure occurs on condition that the walls have opposite sense. An illustration of conditioned erase is shown in FIGURE 6. In FIGURE 6A, strip 11 is shown magnetized alternately in an up-and-down pattern of closure domains 31. The erase Winding 29 is shown such that leg 29a 4lies above domain Wall 33 and leg 2% lies above domain wall 34. For the domain orientation shown, the application ofv a current pulse to winding 29 in the direction shown by the arrow Ic will cause domain walls 33 and 34 to be broughttogether. In'FIGURE 6B the case of the two similar walls is illustrated and in 6C the case of two dissimilar walls is shown. If now a current pulse in the opposite direction is applied to winding 29, similar walls 33 and 3'4- are restored to the original pattern configuration and there has been no change in the stored information, as is shown in FIGURE 6D. When the walls 33 and 34 are dissimilar, they destroy each other when brought together and the subsequent pulsing of winding 29 has no effect on the pattern of FIGURE 5C so that the information stored in walls 33 and 3ft-is erased from the strip 11. This operation may be called conditional erase since erasure occurs only if dissimilar walls are brought together.

Unconditional erase requires that two adjacent walls such as 33 and 34 be removed regardless of sense. This can be accomplished by driving winding 29 with a current large enough to produce the much larger field needed (of the order of 10.0 oersteds) to eliminate domain walls of the same sense. This is an `adequate operating margin between the operations of conditional and unconditional erase.

The use of algebraic summation to perform logic is commonly called majority logic. Inrgeneral, the majority-organ is assumedV to have anodd number of inputs, and an output which is the same as the majority of inputs. Table I sets out the definition of the logical functions o AND and OR considered necessary to Fan-in can be accomplished' in 'two different ways.. In y FIGURES Y'5E-J, one input is on the right and the other Table I X Y "AND onl P P P YP N P NV P P Nk N P N N NV .NV

Assume three inputs to the majority organ to be X, Y, and Z 4andwgive Z a fixed value N. `As shown in Table II, the output is seen by inspection to be the AND of TableI.`

Y Table'II`V X Y Z Output P l?l N P N P N N P N N N N N N Y N Let Z have the constant Value P and the correspondingY output is shown by kTable `III to be OR.

VTable Illr VX Yk Z out- Y,put

. P P VvP P N P P P P N P P N N P Nl It has already been implied. in discussing conditional erase that the wall rotations add algebraically. VIt wasV pointed out that, when two walls of opposite sense are brought together, the resultant is destruction or unwind- 1 ing the rotation back to zero., When two walls of the same' sense are brought; together, a double or 360 wall is formed which Vis separable again. Y

is on the ktnasymmetrical fan-in, while in'FIGURES 5K-R, both inputs areon the left, symmetrical fan-1n'.

The essential difference between .the two lies in the ar- Y rangement of shift Windingsto transfer the domain walls through the Y junction region. The asymmetrical fan-in junction may yrequire a less complex control Winding sysvtern and in addition may lendritself more readily to subsequent logical operations. Y

` Fan-in is somewhatmore diticult' toexecute since the regular sequence of up-and-down Adomains must be preserved.r In order to do so, it appearsnecessary to transfer Walls in pairs from either input channel to the output.

channel. In asymmetrical fan-in, one of these Walls is a dummy inrthat its sense is arbitrary, while in symmetrical fan-in-fboth Walls carry infomation. y

FIGURES V5E through 5J. show a sequence of operations using asymmetrical fain-in.` FIGURE 5E indicates that the input data on channels 1' and 2, a1, a2, etc.,r and b1, b2, Vetc is augmented by the inclusion of dummy walls rl. InlFIGURE 5F, therst data wall 'b1 is shown shifted to the left across the junction with the formation of an rauxiliary wall b; In FIGURE 5G, after the transfer of Wall. b1 completely through the junction, Wall-b 4will be placed-in the output channel while wall b1 has been shifted -nel and the output channel. Finally, ythe'unwanted walls Vd, VZ, c1 and d in the; input channel 2 and unwanted walls vb and Zfin the output channel. are unconditionally erased as vshownl in FIGURE 5]. 'This data wall configuration Sumrnation of any number of wall rotations can be v' accomplishediby applying successive -elds to the Ywalls in alternating UP and DOWN directions. ',Thenal re- ,sult is toV leave only one wall or -an odd numbered group of walls which have .the same rotational senseas the initial. majority. If more than fone wall is lcft,`the

operation of unconditional erase Vcan eliminate all ,but`

one Wall.

The processingof data also requires the'operati'on of transferring data from a single channel into two channels,

called fan-out and themixing of data from: two chanV nels into a single strip, called fan-in." VFan-out is accomplished as vshown'in-FIGURESv SA-D in which an.,V

' arbitrary pattern of domain walls, indicated .asP-and N, are spaced by the usual sequence of domains alter- .nately magnetized in opposite directionsas shownbyfthe.

arrows placed therein. As the domain walls are'shifted to the right by the, application of local'elds, as shownj in FIGURES 5B,'5C, and 5D, two walls appear, one in each'V has the same form asV the initial one of YFIGURE 5E and hence the fan-in can lbe carried out ony the next input data.

The injectedrwa'lls Z and Z can have the sense P-N to produce an AND junctionor NP to produce the OR function. o. Y Y v yThe symmetrical fan-in Voperation is similar. in many respects to the Vasyrrnnetrical case. FIGURE 5K is taken as the initial state; note that the AY data is augumentedl by a dummy wall au. l In FIGURE 5L the wall a0 has been shifted to thelright withthe creation of `Wall a at the junctiom: In FIGURE 5M the a wall has been shifted to theV left into theinputZ channelwhile the Adata has been shiftedvto the right again .with'ao entering the output channel. Y In FIGURE SNfthefA data is again dshifted tothe Vright and as wall a1 crosses the junction wall a", is created. Y In FIGURE 50 the operation of unconditional erase removes unwanted walls a" and a and the data in the output channel, a0, and a1 is shifted'to the right. FIGURES 5P and 5R; show thefb. data being shifted tothe rightv into a position similar .to the initial state OFIGURE 5K. The movementof Walls b1 and b2 across thejunction into theoutput channel with the creationpof unwanted walls andtheir lerasure is accomplished of the output channels; the energy to create the addi-fr tional length of domain wall is generated by energy taken from the current in the shift windings. AThe exactrorientation of the shift windings in order'rtoV maintainl the` required direction ofjmagnetic lield through the Y-shapedY junction may require the usev of auxiliary shift windings to procure a resultant vfield in adesired'direction. Since this is merely a' matter of .design involving the" exact coniguration of magnetic strips employed,-the details are not. Y.

an understanding ofthe principle j kin a manner like unto that employed Vfor A data. After bi and b2 lhaveybeen transferred, the cycle starts over againto mix the input data ask required. The transfer of walls in pairs from inputs land 2 is necessary in 4order to preserve the pattern of up-down spacer domains.r Y By the-method described above, pairs rof Walls tzr-b1,

tlg-a2, etc.` can be formed-in the outputv strip. At this time majority logic as Ydescribed above can' be performed l on these pairs of walls toproduce ythe AND? yor OR logical functions.r However, thereu is an alternative ksequence of operation which can be usedr to produce AND or O R as follows.; The operationof fconditional erase f 1s performed to bring two 'domain walls (eg, rtl-bi) togetherfandthen apart.- 4The data pattern fis' preserved if the twowalls are sirn'ilarand destroyedif the two lwalls are disslrnilar. Next, la writeoo'perationrisV performed by cited above.

magnetization within a moving wall.

applying a field having the proper magnitude to inject a domain in the case the domain walls had been destroyed and a direction such as to generate an N-P or P-N pair depending on whether the function AND or OR is described and on whether the left or right hand wall is to nally represent the result. In the case that the domain walls had not been erased, the write operation cannot change the domain walls since the write field is in a direction ,to preserve the domain pattern, and the original domain wall information pattern is unaffected. The same operations are not performed on the pair [z2-a2 and finally, the extra pair of walls which have been generated, one from operating on tzr-b1, and one from operating on bz-az, are erased unconditionally.

While digital computer logic can be carried out with klogical AND and OR functions, complementation often simplifies the computation. There seems to be a fairly critical relationship between magnetic film thickness and width in which a Neel wall entering a wide region can become two Neel segments in order to minimize the magnetostatic energy associated with the wall. r[his is analogous to the local liux closure generated in cross-tie walls as described by Huber et al. in the paper FIGURES 7A, B, and C represent successive steps illustrating complementation in which the lower Nel segment is the complement of the upper.

The reading operation to detect the sense of rotation of magnetization of the domain wall can be accomplished in several ways. A pick-up loop wound around the strip along the direction of the easy axis of magnetization is oriented to be unaffected by the domains as they are shifting and to sense directly the average direction of This method presents two difficulties: first, the loop should be made of a conductor having a width of the order of the wall thickness, about 10*4 cm.; and second, the small number of spins in a wall produces a very small signal. A second method involves injecting an auxilary wall with a predetermined sense, performing a conditional erase between the data wall and the auxiliary wall, and subsequently reading the resulting domain pattern by inductive pick-up methods. The well-known Kerr magneto-optical effect is still another technique for observing domain patterns.

While the preceding. disclosure has been directed primarily to only a few illustrative embodiments of the present invention, it will be understood that the invention is not restricted to these examples. The system of magnetic domain-wall storage and logic uses spatial rotations of domain wall magnetization to code information and the algebraic addition of these rotations to perform logical functions. To those skilled in the art, the combination of logic elements to make systems containing a large number of storage and logical operations can be extrapolated from the examples given.

What is claimed is:

l. Data processing apparatus comprising, a strip of magnetic film material having an easy axis of magnetization substantially transverse to its length, a source of electrical data pulses in binary form, write windings connected to said source and magnetically coupled to one end of said strip for applying thereto a local switching field at an angle to said easy axis in the plane of said strip to inject domain walls therein having a predetermined sense of rotation of magnetization controlled in accordance with the sense of said data, means for applying local propagation fields in the plane of said strip along said easy axis in the vicinity of domain walls to shift the position of said walls along said tape through a predetermined Zone, an erase winding spaced along said strip from said write winding and adapted when energized to apply local magnetic fields having the same direction simultaneously to two adjacent domain walls thereby bringing said adjacent walls together for one direction of current flow to cause algebraic summation of domain wall rotation, whereby like walls form a double wall of 360 rotation and unlike walls are returned to 0 rotation and for the alternate direction of current flow moving adjacent Walls apart, and timing means for energizing said write windings said propagation means and said erase winding in a predetermined sequence whereby said data is stored and processed along said strip as the controlled sense of rotation of magnetization within domain walls which separate domain zones magnetized in alternate directions along said easy axis.

2. Data processing apparatus comprising, a strip of magnetic film material having an easy axis of magnetization substantially transverse to its length, a source of electrical data pulses in binary form, write windings connected to said source and magnetically coupled toone end of said strip for applying thereto a local switching field at an angle to said easy axis in the plane of said strip to inject domain walls therein having a predetermined sense ot rotation of magnetization controlled in accordance with the sense of said data, means for applying local propagation fields in the plane of said strip along said easy axis in the vicinity of domain walls to shift the position of said walls along said strip through a predetermined zone, an erase winding spaced along said strip from said write winding and adapted when energized to apply local magnetic fields having the same direction simultaneously to two adjacent domain Walls thereby bringing said adjacent walls together for one direction of current flow to cause algebraic summation of domain wall rotation, whereby like walls form a double wall of 360 rotation and unlike walls are returned to 0 rotation and for the alternate direction of current flow moving adjacent walls apart, and timing means for energizing said write windings said propagation means and said erase winding in a predetermined sequency whereby said data is stored and processed along said strip as the controlled sense of rotation of magnetization within domain walls which separate domain zones magnetized in alternate directions along said easy axis, and read-out means located at a point along said strip away from said write windings for detecting the sense of domain wall lrotation as said domain wall is shitted past said read-out means.

3. Data processing apparatus comprising, a plurality of strips of magnetic film, each having an easy axis of magnetization substantially transverse to its length, said strips being arranged to meet at a common junction, a source of electrical binary data pulses, write windings connected to said source and magnetically coupled to said stripsY at points spaced along said strips away from said junction and adapted when energized to apply local switching fields to inject domain walls in the plane of said strips, said domain walls having a controlled sense of rotation corresponding to the sense of said data, means for applying local propagation fields in the plane of each strip in the Vicinity of ydomain walls to shift the position of said walls along each strip through a predetermined zone, means for applying local propagation fields in the vicinity of said common junction to shift the position of domain walls across said junction from one of said strips to another of said strips, erase windings located in the vicinity of said junction and adapted when energized to eliminate unwanted domain walls by applying local fields thereto; auxiliary write windings located in the vicinity of said junction and adapted when energized to inject auxiliary domain walls of predetermined sense of rotation, and timing means for energizing said write windings for said plurality of strips, said strip and junction propagation means, said erase windings, and said auxiliary write windings in a predetermined sequence whereby data is stored, shifted, combined and processed to perform predetermined logic operations thereon.

4. Data processing apparatus comprising, a plurality of strips of magnetic film, each having an easy axis of magnetization substantially transverse to its length, said strips being arranged to meet at a common junction, a source of electrical binary data pulses, write windings connected j and adapted when Yenergized to apply local switching fields to inject Ydomain walls infthe plane of saidstrips, said domain walls having a controlled sense of rotation corre- Y sponding to the sense o'-said/data, 'means for applying local' propagation llields in the plane of Yeach stripY inthe Y vicinity of domain walls to shift the position of said walls along each strip through a predetermined zone, means for applying localpropagation fields in the vicinity Yof said.

common junction to Shift the position Vof domain walls said strips, erase windings located in the vicinity of said alternate directions transverse to said length of said strip,

.rneansforrapplying local propagation elds in the plane Yof. said strip alongsaid easy axisin the vicinityrof domain walls to shift the' position of said Walls along said tape,

` across' said junction from one of said strips to another Yot' Y junction and adapted when energized to eliminate 'un-'H wanted domain wallsby applying local fields thereto; auxiliary write windings located in the vicinity of said junction and adapted when energizedfto inject auxiliary domain-.Walls Yof predetermined sense of rotation, timing means for energizing said. write windings for said plurality of strips, said strip and junction propagation means, said erase windings,` and said auXiiiary write windings in a predetermined sequence whereby vdata is stored, shifted, ccm-Y Ybined and processed to performY predetermined logic operations thereon, andread-out means located along at least oneof said strips at a pointl remote from said junction for detecting the sense of domain wall magnetization las and means for energizingrsaid write Windings'and said propagation'means in a predetermined sequence whereby data is stored in ysaid strip as the controlled sense of rotation of interdomain wall magnetization.

1 v6. Data processing apparatus comprising, a current source, va binary 'data source of positive and negative electricalpulses, attliin lm strip of magnetic material having anV easy axis of magnetization substantially transverse to `its'length, a pair of writewindings magnetically coupled to said strip, said pair offwindings being arranged to cross said strip at opposite iacute angles oriented with respect to said Yeasy axis so that one of said pair of windings is adaptedto apply a local switching field'in the plane otrsaid strip producing domain injectionwith an opposite sense of rotation of domain wail magnetization Vfrom that produced bythe second of said pair of windings, means for energizing one of said ypair of windings from saidcurrent source inaresponse tol positive pulses from said data source vand energizing they second of said said domain Ywallsrare shifted pastl said readfout location.

5. Data processing apparatus comprising, a .current source, a binary datasource of positiveV and negative electrical pulses, a thin film strip of magneticjmaterial hav i ing an easy axis of magnetization substantially transverse to its length, a pair of write windings Vmagnetically `coupled to said strip, said pair otwindingsbeingV arrangedV to cross said strip at opposite acute .angles orientedlwith respect lto said. easydaxisvsoV that' one of saidr pair of windings is adapted to apply a local switching field in the plane of saidrstrip producingV domain injection Withan Y opposite sense of lrotation of .domain wall/magnetization f from that produced by the second of said pairl of windings, `means for energizingrone of said pair of windingsl from saidcurrent source in responseto positive. pulses Y from said data source andenergizingthe secondof said pair of windings from said current source fin response to negative pulses fr'orn'said data source toinject domain,

walls in saidstrip having'a predetermined sense of rotation of'intefrdomain wall magnetization controlled in'ac-,

cordance with the sense of said data pulses, means for alternating thedirection ofY current flow insaid ywrite pair ofwindings from said current source in response to negative pulses from said data source to inject domain walls'in said strip having a predetermined sense Vof rota- 'tion ofrinterdomain wall magnetization controlled in accordance withthe senseoir said data pulses, meansfor alternating the direction ,of current ilow'in said write u Y windings from saidrcurrent source to provide for the injection of successive magneticl domains magnetized in I alternate directions transverse to said length of said strip,

means Vfor applying local propagation lields in the plane of saidl strip along'saidl easy axis in the' vicinity of domain .wail's'to'shift thel position ofsaidvwalls along said tape, 3 means for energizing said write windings and said vpropagation means inta predetermined sequence'whereby data tis stored in said stripras the controlled sense of rotation of vinterdomain wallVV magnetization, Vand read-'out means located at a point along said stripfre'mote from said write ywindings-for detecting thersense of interdomain wall rotation as said domain wall is shifted kpast said read-out Y means. i Y v. f

ReferencesCited by the Examiner l y y UNITEDISTATES .PATENTS .Y 2,872,663l 2/59 Kelneret al. 340;-174 3,068,453v 12/62 Broadbent Y Y r '340-174 windings from'said currentsource to provide for the in- I jection ofr successive magnetic Ydomains magnetized in IRVIVGVVL. SRAGOW, Primm); Examiner. 

1. DATA PROCESSING APPARATUS COMPRISING, A STRIP OF MAGNETIC FILM MATERIAL HAVING AN EASY AXIS OF MAGNETIZATION SUBSTANTIALLY TRANSVERSE TO ITS LENGTH, A SOURCE OF ELECTRICAL DATA PULSES IN BINARY FORM, WRITE WINDINGS CONNECTED TO SAID SOURCE AND MAGNETICALLY COUPLED TO ONE END OF SAID STRIP FOR APPLYING THERETO A LOCAL SWITCHING FIELD AT AN ANGLE TO SAID EASY AXIS IN TH E PLATE OF SAID STRIP TO INJECT DOMAIN WALLS THEREIN HAVING A PREDETERMINED SENSE OF ROTATION OF MAGNETIZATION CONTROLLED IN ACCORDANCE WITH THE SENSE OF SAID DATA, MEANS FOR APPLYING LOCAL PROPAGATION FIELDS IN THE PLANE OF SAID STRIP ALONG SAID EASY AXIS IN THE VICINITY OF DOMAIN WALLS TO SHIFT THE POSITION OF SAID WALLS ALONG SAID TAPE THROUGH A PREDETERMINED ZONE, AN ERASE WINDING SPACED ALONG SAID STRIP FROM SAID WRITE WINDING AND ADAPTED WHEN ENERGIZED TO APPLY LOCAL MAGNETIC FIELDS HAVING THE SAME DIRECTION SIMULTANEOUSLY TO TWO ADJACENT DOMAIN WALLS THEREBY BRINGING SAID ADJACENT WALLS TOGETHER FOR ONE DIRECTION OF CURRENT FLOW TO CAUSE ALGEBRAIC SUMMATION OF DOMAIN WALL ROTATION, WHEREBY LIKE WALLS FORM A DOUBLE WALL OF 360* ROTATION AND UNLIKE WALLS ARE RETURNED TO 0* ROTATION AND FOR THE ALTERNATE DIRECTION OF CURRENT FLOW MOVING ADJACENT WALLS APART, AND TIMING MEANS FOR ENERGIZING SAID WRITE WINDINGS SAID PROPAGATION MEANS SAID ERASE WINDING IN A PREDETERMINED SEQUENCE WHEREBY SAID DATA IS STORED AND PROCESSED ALONG SAID STRIP AS THE CONTROLLED SENSE OF ROTATION OF MGNETIZATION WITHIN DOMAIN WALLS WHICH SEPARATE DOMAIN ZONES MAGNETIZED IN ALTERNATE DIRECTIONS ALONG SAID EASY AXIS. 